Java servlet technology lets you define HTTP-specific servlet classes. A servlet class extends the capabilities of servers that host applications that are accessed by way of a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers.
In the Java EE 6 platform, new Java servlet technology features include the following:
Asynchronous support
Ease of configuration
Pluggability
Enhancements to existing APIs
Annotation support